Numerous systems have been developed that provide a network of alarm units for detecting a hazardous condition. Typically in these systems, the individual alarm units are interconnected to form the network to allow each alarm unit in the network to activate a respective horn when a hazardous condition is detected by any one of the alarm units.
In a network of multiple alarm units, it may be difficult to identify the location of the hazardous condition if a person cannot pinpoint which alarm unit triggered the system. As discussed below, several interconnected alarm systems have been developed that utilize a flashing light source (e.g., light emitting diode (LED)) on the triggering alarm unit to identify the alarm unit that detected the hazardous condition and triggered all of the interconnected alarm units within the network to activate their respective horns.
However, a person may not be able to recognize a flashing light source if the alarm unit is not in the line of sight of the viewer. For instance, a flashing light source can be easily missed by a person if the alarm unit is blocked by walls, ceiling fans, exit signs, or other obstructions. Likewise, a flashing light source may go unnoticed by a person with poor eyesight or if the person has his or her back turned to the alarm unit.
Moreover, in order to identify all of the alarm units that detected the hazardous condition (or to check the alarm units for false alarms), the person must go to every room having an alarm unit to determine whether the flashing light source has been activated. This task is magnified when there are a large number of alarm units in the network. Unless the alarm units are visible from a hallway, a person cannot merely walk down the hallway and look into every room to determine whether the alarm units are flashing a light source.
Another drawback of prior alarm systems is the lack of a quick and efficient means for resetting or clearing the light sources on the alarm units after the alarm unit that triggered the network of interconnected alarm units to activate their respective horns has been identified. Specifically, the light sources can only be reset by manually depressing a reset switch located on each individual alarm unit. The task is magnified when there are a large number of alarm units in the network. In large multi-story buildings having numerous alarm units, a substantial amount of time and effort is needed to reset all of the light sources in the network. A person is required to go to each and every room having an alarm unit therein, and manually reset each individual alarm unit having a flashing light source. Further, it is often difficult and time consuming to manually depress the reset switch on every alarm unit when the alarm units are positioned on or near the ceiling in an effort to detect rising smoke.
U.S. Pat. No. 4,349,812 to Healey is an example of a system having a plurality of alarm units. Each alarm unit is connected to a central control panel that includes a display board having a light source associated with each alarm unit. When an alarm unit detects a hazardous condition, the alarm unit sends a signal that latches an indicator circuit associated with the alarm unit, which in turn activates a light source on the display board for the alarm unit.
A person must physically go to the central control panel and visually check the display board to identify the alarm units that detected the hazardous condition. This may be difficult if the central control panel is not easily accessible (e.g., due to the hazardous condition) or if the person does not know where the central control panel is located within the building. Moreover, in an emergency situation where time is of the essence, it may be difficult to access the central control panel in a timely manner.
U.S. Pat. No. 6,353,395 to Duran provides an example of a network of interconnected alarm units, wherein each alarm unit has a light source that can be manually activated if the alarm unit has detected a hazardous condition. More specifically, a latch within the alarm unit that detected the hazardous condition and triggered all of the interconnected alarm units within the network to activate their horns (referred to herein as the “triggering alarm unit”) is set to a latched state when the triggering alarm unit detects a hazardous condition. Subsequently, if a test switch is actuated on the triggering alarm unit, a light source (i.e., pulsed illumination of an LED) is activated on the triggering alarm unit for a predetermined period (e.g., 10 minutes). The light source requires manual activation of the test switch on the triggering alarm unit to identify whether the alarm unit has detected the hazardous condition. Thus, a person must test each individual alarm unit in the network in order to identify all of the alarm units that triggered the network alarm. In a large building, a considerable amount of time and effort may be required before a single triggering alarm unit is located, even if the user chooses not to test every alarm unit in the building. In order to reset all of the latches in the network, the reset switch in each and every triggering alarm unit must be pressed. As such, the person must reset each individual alarm unit to ensure that all of the latches within the network are reset.
U.S. Pat. No. 7,075,444 to Tanguay discloses a network of alarm units connected by an interconnect line. When a hazardous condition is detected by the triggering alarm unit, a signal is sent through the interconnect line causing all of the alarm units in the network to sound their horns and/or flash their light sources. During the alarm condition (i.e., when the hazardous condition is being detected), an alarm origination test can be performed to identify the triggering alarm unit. Upon actuation of a test switch on any of the interconnected alarm units, the alarm origination test disables the horns and/or flashing light sources on all of the alarm units except for the alarm unit that is currently sensing the hazardous condition.
More specifically, the alarm origination test disables the interconnect line between the triggering alarm unit and the non-triggering remote alarm units. Thus, only the horn/light source on the alarm unit actually detecting the hazardous condition remains active. The horn/light source on the triggering alarm unit is only active when presently “sensing” the hazardous condition. As such, the triggering alarm unit can only be identified when the hazardous condition is present. It is advantageous to have the capability of latching a hazardous condition detection event into memory and subsequently testing the alarm units after the hazardous condition has been eliminated. The alarm units of Tanguay '444 do not include internal memory that latches upon detection of the hazardous condition, wherein the triggering alarm unit is identified based on the latched memory. Moreover, a means for resetting or clearing memory in the alarm units is not provided. Many of the features discussed above conform with established regulations and standards, e.g., Underwriters Laboratory Specification (UL) 217.